A description of a women who enjoys casual sex and seeks it fairly frequently. Created to replace the nasty term "slut" because sex is good, wanting sex is normal, casual sex is fun, and calling women "sluts" discourages them from having more sex. Courty is a much nicer sounding word, derived from "courtesan", an old romantic term for the mistress of a king or other high class person, or a high class prostitute.

"She's shagged all three of them? Damn, what a legend"
"Yeah, she's a total courty"